Exhaust gas turbochargers are usually equipped with rolling bearings which, because of the high rotational speeds, have to be lubricated and cooled by large quantities of injected oil whereas, during starting and at low rotational speeds, they can operate without any oil at all. The quantity of oil injected needs to be accurately determined and should increase approximately in proportion to the rotational speed. The injection of the oil into the rolling body race of the rolling bearing should take place near the bearing inner ring. The lubricating oil is sucked from the oil sump by a centrifugal pump located on the shaft of the turbocharger and is passed through the rolling bearing. Part of the oil can be injected for cooling purposes directly onto the thermally heavily loaded parts.
Self-priming centrifugal lubricating oil pumps of the this type are known, for example, from the Swiss Pat. No. 451,714. In this device, the lubricating oil pump is attached to one end of the turbocharger shaft and, for this reason, can only be used in turbochargers with external bearings because this system depends on a relatively small internal diameter of the rotating oil ring relative to the bearing diameter, which, for design reasons, cannot always be attained in turbochargers with internal bearings.
The lubrication of the shaft bearing of an exhaust gas turbocharger with internal bearings is normally carried out by means of an external pump, for example a gear or piston pump. Such a pump requires a separate drive and much space; in addition, it requires maintenance and the failure rates of individual components are not negligible.